1. Field of the Invention
The present invention relates to a method for controlling the tire pressure in multiple-axle vehicles whose wheels are equipped with pneumatic tires and speed sensors that supply an evaluation unit with signals indicative of the speed of the respective wheel, by    (a) determining simultaneously the speed of a right-hand wheel and of a lefthand wheel mounted on a common axle;    (b) determining the deviation between the two speeds;    (c) reducing the deviation in speed by a correction value representative, during a cornering motion, of that component of the deviation in speed between the right-hand wheel and the left-hand wheel which is due to the cornering motion; and    (d) indicating the corrected deviation in speed, or of a signal derived therefrom, at least when the corrected deviation in speed exceeds a given threshold value.
2. Description of Related Art
It has been known in connection with vehicles, the wheels of which are equipped with an anti-block system (ABS), that the ABS can be used also for deriving information on the tire pressure. This is due to the fact that any drop in tire pressure will reduce the rolling radius of the wheel so that the spin velocity of the wheel will increase as the tire pressure decreases—related to a given vehicle speed. Anti-block systems comprise speed sensors on each wheel which monitor the spinning velocity of the wheels in order to permit early detection of any blocking risk for the respective wheel. Anti-block systems therefore supply a signal for each wheel that indicates the spinning velocity of the respective wheel. An evaluation unit provided in the vehicle, which receives other signals as well, derives from the speed signals information of the rolling radius and, thus, the tire pressure of the respective wheel. However, the spinning velocity of a wheel depends not only on the rolling radius and the vehicle speed, but also on the driving condition, i.e. whether the wheel is running straight ahead or is cornering. When cornering, the outer wheels, relative to the curve, have to run a longer way than the inner wheels, relative to the curve, so that any difference between the speed of the right-hand wheel and the speed of the left-hand wheel mounted on one and the same axle may not necessarily, or exclusively, be due to differences in tire pressure, but may be caused also by a cornering motion of the vehicle. It has, therefore, been known to supply the evaluation signal unit with additional signals from a steering angle transmitter. The steering angle transmitter picks up any rotary movements of the steering column of the vehicle and signals them to the evaluation unit. The relation between the radius of curvature and the steering angle being known, it is possible for the evaluation unit to calculate from the signal received from the steering angle transmitter the radius of the curve along which the vehicle is moving. That radius then serves as a basis for calculating the difference in speed between a right-hand wheel and a left-hand wheel on a common axle that is due to the cornering movement. If the difference in speed measured is corrected by that value, and if a difference in speed is still left after such correction, then this is taken as a measure for the deviation between the tire pressure of the right-hand wheel and the left-hand wheel, which is then signaled to the driver in order to warn him when it exceeds a given threshold value.
In the case of vehicles where the wheels cannot be steered, no steering signal can be obtained for correcting any speed difference between a right-hand wheel and a left-hand wheel during cornering of the vehicle. This speaks against the use of an ABS-supported tire pressure control solution in vehicles that do not have any steered wheels. This is true in particular for commercial vehicle trailers. In the case of such trailers, tire pressure is normally monitored, while the vehicle is in motion, using pressure sensors provided on each wheel for transmitting the detected tire pressure value to a receiver placed in the vehicle which then evaluates the pressure signals and signals to the driver any abnormal pressure or abnormal pressure curve that may be detected. Although tire pressure control systems using pressure sensors placed on wheels permit the pressure to be monitored exactly, they unfortunately are more expensive than ABS-supported tire pressure control systems.